The present invention is directed generally to epoxy nitrile coating compositions for use as protective surface coatings on various substrates such as metal, wood, plastic, paper and the like. This invention relates to novel 100 percent solids epoxy nitrile coating systems. In another aspect, the invention relates to novel coating compositions and the process for producing the coating compositions which coatings have excellent appearance, superior adhesion, excellent hardness, superior barrier properties, high gloss and excellent corrosion resistance.
The use of epoxy coatings are known in the art. Representative examples of epoxy resin coating compositions and their preparation include those disclosed in U.S. Pat. No. 3,530,096. Epoxy coatings exhibit high adhesion, toughness and chemical resistance. Most epoxy coating systems used today are solvent based or water based. Solvent based coatings are disadvantageous in that large amounts of volatile organic solvents are present. These solvents may be costly and hazardous. The solvents must be removed from the final coatings which requires considerable thermal energy. Further, if hazardous, the solvents must be recovered or incinerated as they may not be exhausted into the environment. Water based coatings are disadvantageous in that they are not continuous and have been found to contain more pinholes and voids than the solvent based coatings.
As a result, the search for an essentially solvent-free coating process has led to the use of solventless systems. The advantages of a solventless epoxy coating system includes the minimization of surface defects due to the absence of solvents and excellent heat and chemical resistance. However, these coating compositions have increased sensitivity to humidity causing blushing and have poor impact resistance end flexibility.
Additionally, nany epoxy coating systems also require high curing temperatures, in excess of 175.degree. C. Further, epoxy coating systems do not exhibit particularly good moisture barrier properties.
The use of nitrile resin coatings are known in the art. Nitrile resin coatings exhibit high moisture barrier properties. However. nitrile resin coatings exhibit poor adhesion to the substrate when cured at temperatures below 200.degree. C. Representative examples of nitrile resin coating compositions and their preparation include those disclosed in U.S. Pat. Nos. 4,379,875 and 4,374,948. These patents teach that the nitrile resin coatings are thermally cured. Thermally cured nitrile resin coating processes require a high thermal energv input.
The current approach as found in U.S. Pat. No. 3,530,096 is to synthetically introduce a nitrile functional group into an epoxy resin by substituting the hydroxyl functional group with the nitrile functional group. The process uses inert solvents such as tolune or xylene for the reaction of substituting nitrile groups into the epoxy resin. This process however, results in a coating system which suffers from severe cratering and consequently poor corrosion protection.
A general discussion as to how coatings function is available in, Kirk-O thmer Encyclopedia of Chemical Technology, Vol 7, p. 113"Corrosion and Corrosion Inhibitors", John Wiley and Sons, Inc., 1979, and L. Blecher, D. H. Lorenz, H. L. Lowd, A. S. Wood and D. P. Wyman, "Handbook of Water-Soluble Gums and Resins", R. L. Davidson, ed., McGraw Hill, N.Y. 1980.
It is an object of this invention to provide epoxy nitrile coating compositions in a 100 percent solids, solvent free system to avoid use of cyclable solvents. It is another object of this invention to combine the excellent adhesion, chemical resistance and durability of the epoxy function with the verv good moisture barrier properties of the nitrile function. It is another object of this invention to provide hard epoxy nitrile coating compositions which are corrosion resistant, prevent metal corrosion and have no pinholes or voids.
These and other objects, together with the advantages over known methods shall become apparent from the specification which follows and are accomplished bv the invention as hereinafter described and claimed.